That's probably because you aren't using X.org's clipboard manager but something different like Klipper (KDE) or Gnome clipboard manager. It's kinda easy to imagine how annoying it can be: You copy an url from a browser and close it and then try to paste it but woops... you can't. You try to go back but you can't remember what the url was. Have fun finding it again.
It's called "browser history" ... in any case, yeah, this is an annoying bug
Don't get me wrong, I know things are currently being developed, but when are we going to be able to run things like KDE and Gnome on Wayland?
I don't know about Gnome, but KDE won't be on wayland until Qt 5 is out, which is the first version of Qt that will have native Qt support. I think kwin developers were waiting to port to wayland until the API stabilized.
You do know that the same "design flaw" is part of most operating systems (including Windows), don't you?
Of course Windows comes with some sort of a clipboard manager by default since a long time, but AFAIK that is only used if the application uses it explicitly (which for some use cases is a better solution, but of course it won't work if the application has no support for it).